Stacked Common-Base vs Common-Emitter mmWave PA Cells and 68–105 GHz Broadband Asymmetrical PA in 250nm InP HBT

Abstract

In this paper, we perform a comparative analysis between stacked common-emitter (SCE) and stacked common-base topologies (SCB) for high efficiency and broadband millimeter-Wave (mmWave) power amplifiers (PAs) in 250 nm InP-based heterojunction bipolar transistor (HBT) technology. We propose an analytical approach to design stacked PA cells accounting for complex load impedance and intra-matching between stacked transistors to allow optimal loadpull operation of both the devices in the stack. We demonstrate how SCB cell can allow higher gain, mitigated power and efficiency trade-off and linearity, when compared to more well-established SCE cells at higher mmWave frequencies. The designed SCB and SCE cells achieve a measured gain of 11.8 dB/6dB gain, 33%/34% peak PAE, 16.8%/14.5% PAE at 6-dB back-off, and Psat of 18.7 dBm/19.6 dBm at 90 GHz. The SCB PA demonstrates superior linearity, and achieves an EVM of 2.38% at 11.8-dBm average power supporting 3 Gbps 64-QAM. The SCB PA achieves 17.9-18.9-dBm Psat across 80–110 GHz and is one of the highest efficiency, broadband and linear PAs in W-band using InP technology. Utilizing the PA cells, we demonstrate an asymmetrical broadband power combining circuit for high efficiency combining across a large relatively bandwidth. The PA operates across a 68–105 GHz $P_{sat,3dB}$ bandwidth with 21.5 dBm peak saturation power and 24% peak PAE.

Keywords

• Asymmetrical combiner
• broadband
• common-base
• InP HBT
• millimeter-Wave (mmWave)
• power amplifiers (PAs)